An exposure device mounted in an image forming apparatus typically includes a light source emitting a laser beam, a collimator lens converging the laser beam emitted from the light source, an imaging lens, a polygon mirror (rotating polygon mirror) deflecting the converged light beam, and a reflecting mirror reflecting the laser beam, deflected by the polygon mirror, onto a photoreceptor drum as an object to be exposed. The reflecting mirror is located on the most downstream side of the travelling direction of the laser beam in the exposure device. The angle of a reflection surface of the reflecting mirror can be adjusted by a position adjustment unit of a mirror support portion. For example, the reflecting mirror has two mirror support points at one end in a longitudinal direction of the reflection surface (or a surface opposite to the reflecting surface) and one mirror support point at the other end. The attitude of the reflecting mirror is determined by the relative position among the three mirror support points. The reflecting mirror is fixed by receiving a load in an opposite direction as a mirror support direction, using a leaf spring and so on. One of the two mirror support points is positioned by, for example, the projecting amount of the tip of an adjustment screw. The angle of the reflecting mirror can be adjusted by positioning the mirror support point.
However, when the angle of the reflecting mirror is adjusted in the prior art, the adjustment screw is required to be inserted from a direction at right angles to a mirror surface. Accordingly, in conventional exposure devices, since a screw hole is required to be formed obliquely with respect to a housing, a mold structure is complicated, or an extra component corresponding to the adjusted angle is required to be provided. Thus, when the exposure apparatus has a plurality of reflecting mirrors, and when the reflecting mirrors are adjusted to different angles, there is a problem that a screw hole is required to be formed in a housing in accordance with each angle, or an extra component corresponding to the adjusted angle is needed.